linux-kernel - Re: [patch 00/17] CFS Bandwidth Control v7.1

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Date:	Thu, 07 Jul 2011 19:08:57 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	linux-kernel@...r.kernel.org,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Hu Tao <hutao@...fujitsu.com>
Subject: Re: [patch 00/17] CFS Bandwidth Control v7.1

On Thu, 2011-07-07 at 09:52 -0700, Andi Kleen wrote:
> Peter Zijlstra <a.p.zijlstra@...llo.nl> writes:
> >
> > +static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
> > +               unsigned long delta_exec)
> > +{
> > +       if (!cfs_rq->runtime_enabled)
> > +               return;
> > +
> > +       cfs_rq->runtime_remaining -= delta_exec;
> > +       if (cfs_rq->runtime_remaining > 0)
> > +               return;
> > +
> > +       assign_cfs_rq_runtime(cfs_rq);
> > +}
> >
> > generate a call, only to then take the first branch out, marking that
> 
> You would need a *LOT* of calls to make up for 9%.
> 
> Maybe it's something else? Some profiling first before optimization
> is probably a good idea.

This is the 1.5% case where the feature is compiled in but not used.
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